Electrical Engineering ⇒ Topic : Rating of Electrical Devices by Power

Rating of Electrical Devices by Power

Electrical irons, refrigerators, TV sets, electric bulbs and motors are examples of electrical devices that are rated in watts. The power rating of a device indicates the rate at which the device converts electrical energy into other forms of energy,such as heat, light or motion. For example, a 100 W lamp will give out more light than a 40 W lamp, because it converts more electrical energy into light.In addition to indicating a device's ability to do work, its power rating (in watts) can also indicate its operating limits. These power limits generally indicate the maximum or minimum safe voltages or currents which can be applied to the device. In cases where no specific operating voltage is indicated on the device, its limits are given directly in watts, as in resistors. A resistor may be used in circuits with widely different voltages. However, a resistor has a maximum current limit for each voltage applied to it. The product of the voltage and current of the resistor gives its wattage. Thus, the resistors are rated in watts, in addition to their resistance (in ohms). Similarly, an electric iron, a heater used for cooking or a television set are also rated in watts, in addition to the voltage that should be applied to it. On the other hand, fuses which are used to protect devices in electrical circuits are rated for current in amperes. Fuses of different types and sizes are widely in use nowadays.